I don't know but it seems to me that it could also be to work around when their domain gets blacklisted as spam. (i.e. https://stackoverflow.com/questions/32184

I don't know but it seems to me that it could also be to work around when their domain gets blacklisted as spam. (i.e. https://stackoverflow.com/questions/32184742/do-subdomains-protect-a-domains-reputation-when-sending-emails https://stackoverflow.com/questions/32184742/do-subdomains-p...)